[BUG] [Python] Fix autoset constants Python code for default query string value (#19138)

* _query_params is list, not dict

* Add test

modules/openapi-generator/src/main/resources/python/api.mustache

@@ -176,7 +176,7 @@ class {{classname}}:
         {{#constantParams}}
         {{#isQueryParam}}
         # Set client side default value of Query Param "{{baseName}}".
-        _query_params['{{baseName}}'] = {{#_enum}}'{{{.}}}'{{/_enum}}
+        _query_params.append(('{{baseName}}', {{#_enum}}'{{{.}}}'{{/_enum}}))
         {{/isQueryParam}}
         {{#isHeaderParam}}
         # Set client side default value of Header Param "{{baseName}}".

modules/openapi-generator/src/test/java/org/openapitools/codegen/python/PythonClientCodegenTest.java

@@ -528,5 +528,6 @@ public class PythonClientCodegenTest {
                 .get(Paths.get(output.getAbsolutePath(), "openapi_client", "api", "hello_example_api.py").toString());
         assertNotNull(apiFile);
         assertFileContains(apiFile.toPath(), "_header_params['X-CUSTOM_CONSTANT_HEADER'] = 'CONSTANT_VALUE'");
+        assertFileContains(apiFile.toPath(), "_query_params.append(('CONSTANT_QUERY_STRING_KEY', 'CONSTANT_QUERY_STRING_VALUE'))");
     }
 }

modules/openapi-generator/src/test/resources/3_0/java/autoset_constant.yaml

@@ -21,6 +21,13 @@ paths:
             type: string
             enum:
             - CONSTANT_VALUE
+        - name: CONSTANT_QUERY_STRING_KEY
+          in: query
+          required: true
+          schema:
+            type: string
+            enum:
+              - CONSTANT_QUERY_STRING_VALUE
         - name: name
           in: path
           required: true
@@ -39,4 +46,4 @@ components:
       type: object
       properties:
         message:
-          type: string
+          type: string